Disk player, and turntable incorporating self-compensating dynamic balancer, clamper incorporating self-compensating dynamic balancer and spindle motor incorporating self-compensating dynamic balancer adopted for disk player

ABSTRACT

A disk player having a self-compensating dynamic balancer which can limit internal vibrations generated by an eccentric center of gravity of a disk, and a turntable, a clamper and a spindle motor which incorporate a self-compensating dynamic balancer. The self-compensating dynamic balancer is formed integrally with rotating members in a disk player; that is, a turntable, a clamper and/or a rotor of a spindle motor. The self-compensating dynamic balancer includes at least one race which is integrally formed with the rotating member and rotates around a rotational shaft, a mobile unit which is located in the race to be capable of moving, and a cover member for covering an opening of the race. Thus, internal vibrations occurring due to the eccentric center of gravity of the disk can be effectively limited by the self-compensating dynamic balancer in which the mobile unit is disposed far away from the center of orbital rotation by a centrifugal force during rotation thereof.

This is a divisional of application Ser. No. 08/947,895 filed Oct. 9,1997, the disclosure of which is incorporated herein by reference.Application Ser. No. 08/947,895 was filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C. §119(e)(1) of the filing dates ofProvisional Application Nos. 60/027,987 and 60/040,768 filed on Oct. 9,1996 and Mar. 14, 1997, respectively, pursuant to 35 U.S.C. §111(b).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk player, and a turntable, aclamper and a spindle motor which are adopted for the same and, moreparticularly, to a disk player having a self-compensating dynamicbalancer for restricting internal vibrations generated due to aneccentric center of gravity of a disk, and a turntable incorporating theself-compensating dynamic balancer, a clamper incorporating theself-compensating dynamic balancer and a spindle motor incorporating theself-compensating dynamic balancer which are adopted for the same.

2. Description of the Related Art

In general, a disk player records and/or reads information onto and/orfrom a recording medium such as a compact disk (CD), a CD-ROM and adigital versatile disk (DVD). Due to its sensitivity, the disk player isrequired to protect the disk and optical pickup from external impactsand internal vibrations.

A typical disk player, as shown in FIG. 1, includes a deck base 10hinge-coupled to a housing (not shown) to be capable of rotatingvertically, a deck plate 20 coupled to the deck base 10, a spindle motor21 installed at the deck plate 20 for providing a rotational force to adisk 1, a turntable 23 coupled to a rotational shaft 22 of the spindlemotor 21 for accommodating the disk 1, a clamper 40 installed on theinner surface of the upper portion of the housing to face the turntable23 for securing the disk 1 placed on the turntable 23, and an opticalpickup 25 coupled to the deck plate 30 to be capable of moving acrossthe disk 1 for performing recording and reproduction operations. Thedisk player includes buffering members 30 disposed between the deck base10 and the deck plate 20 to prevent the external vibrations transferredthrough the deck base 10 from being transferred directly to the deckplate 20, the spindle motor 21 and the optical pickup 25. The bufferingmembers 30 are formed of a material such as soft rubber or polyurethanewhich can absorb external impacts.

The disk player adopting the buffering members 30 as above caneffectively protect the driving of the disk 1 and the optical pickup 25from external impacts. However, a method of dampening internalvibrations generated by the rotation of the spindle motor 21 due to aneccentric center of gravity of the disk is not taken into consideration.In such a case, the eccentric center of gravity of the disk is caused bya discrepancy between the rotational center of the disk and the centerof gravity of the disk due to errors in the manufacturing process of thedisk. Thus, the rotational shaft of the spindle motor 21 exhibits anorbital revolution due to wobbling of the rotational shaft.

Such orbital revolution of the rotational shaft of the spindle motordoes not effect a low-speed disk player such as a 1X or 2X type.However, in the case of a high-speed model such as a 6X, 8X, 12X, 20X or24X type, the effects of the orbital revolution of the rotational shaftof the spindle motor become serious making the recording/reproducing ofinformation difficult.

To overcome the above problems, in a conventional high-speed diskplayer, the mass of the deck plate where the spindle motor is installedis increased or the rigidity of the buffering members is increased toreduce movements of the deck plate due to the eccentric center ofgravity of the disk.

However, not only is the deck plate having increased mass inappropriatefor a high speed rotation, but also the costs of the product increaseand miniaturization of the product is hindered. Also, when the rigidityof the buffering members is increased, it is not possible to effectivelydampen the external impacts or vibrations.

SUMMARY OF THE INVENTION

To solve the above problems, it is a first objective of the presentinvention to provide a disk player in which external vibrations can bereduced and also internal vibrations generated due to an eccentriccenter of gravity of a disk can be limited without an increase inweight.

It is a second objective of the present invention to provide a turntableincorporating a self-compensating dynamic balancer, which is employed ina disk player so that the internal vibrations due to an eccentric centerof gravity of a disk can be limited.

It is a third objective of the present invention to provide a clamperincorporating a self-compensating dynamic balancer, which is employed ina disk player so that the internal vibrations due to an eccentric centerof gravity of a disk can be limited.

It is a fourth objective of the present invention to provide a spindlemotor incorporating a self-compensating dynamic balancer, which isemployed in a disk player so that the internal vibrations due to aneccentric center of gravity of a disk can be limited.

Accordingly, to achieve the first objective, there is provided a diskplayer comprising a deck base, a deck plate elastically coupled to thedeck base, at least one buffering member interposed between the deckbase and the deck plate for protecting the deck plate from externalimpacts, a spindle motor having a rotational shaft and being mounted tothe deck plate for providing a rotational force to a disk, a turntablemounted to the rotational shaft of the spindle motor for accommodatingthe disk, a damper for holding the disk in place on the turntable, anoptical pickup installed at the deck plate to be capable of movingacross the disk, and a self-compensating dynamic balancer mounted to atleast one among members which are rotated by the rotational forceprovided by the spindle motor, the center of gravity of theself-compensating dynamic balancer being located opposite to that of thedisk with respect to the rotational shaft of the spindle motor by acentrifugal force generated during rotation of the disk.

To achieve the second objective, there is provided a turntableincorporating a self-compensating dynamic balancer adopted in a diskplayer comprising a placing member having a coupling hole which iscoupled to a rotational shaft of a motor and a surface on which a diskis placed, the placing member being rotated by rotation of the motor, acoupling protrusion which is formed on the placing member to projecttherefrom and into which the center hole of a disk fits, at least onecircular race which is formed in the placing member and rotates aroundthe rotation center of the placing member, a mobile unit which is placedinside the race to be capable of moving, a cover member to cover anopening of the race.

To achieve the third objective, there is provided a clamperincorporating a self-compensating dynamic balancer adopted in a diskplayer comprising a damper main body, a pressing unit which is installedat the clamper main body for pressing a disk placed on a turntable, atleast one circular race which is formed in the clamper main body androtates around the center of rotation of the damper main body, a mobileunit placed inside the race to be capable of moving, and a cover memberwhich covers an opening of the race.

To achieve the fourth objective, there is provided a spindle motorincorporating a self-compensating dynamic balancer adopted in diskplayer comprising a rotational shaft, a motor base having a through holein which the rotational shaft is rotatably inserted, a stator fixedlyinstalled at the motor base and having a yoke and a coil wound aroundthe yoke, a rotor having a case which is fixed to an end of therotational shaft and encloses the stator, and a magnet which is fixedinside the case to face the yoke, at least one circular race which isintegrally formed with the case and rotates around the center ofrotation of the rotational shaft, a mobile unit located inside the raceto be capable of moving, and a cover member which is coupled to anopening of the race for sealing the inner space of the race.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objectives and advantages of the present invention will becomemore apparent by describing in detail preferred embodiments thereof withreference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view schematically illustrating aconventional disk player;

FIG. 2 is an exploded perspective view illustrating a disk playeraccording to an embodiment of the present invention;

FIGS. 3A, 3B and 3C are diagrams showing the relationship between aneccentric center of gravity position of a disk, the position of arotational shaft and the center of rotation respectively according todifferent rotation speeds of the disk;

FIGS. 4A and 4B are perspective views illustrating a first embodiment ofa self-compensating dynamic balancer which is employed in a disk playeraccording to the present invention;

FIG. 5 is a cross sectional view of the self-compensating dynamicbalancer shown in FIG. 4 when a rigid body is used as a mobile unit;

FIG. 6 is a cross sectional view of the self-compensating dynamicbalancer shown in FIG. 4 when a rigid body and a fluid are used as themobile unit;

FIGS. 7 and 8 are cross sectional views of self-compensating dynamicbalancers including first and second races, respectively;

FIGS. 9 through 12 are cutaway perspective views schematicallyillustrating the shapes of a rigid body which is used as the mobile unitfor the self-compensating dynamic balancer according to the embodimentof the present invention;

FIGS. 13 through 16 are sectional views schematically illustrating therace and a cover member of the self-compensating dynamic balanceraccording to the embodiment of the present invention;

FIG. 17 is a sectional view illustrating a second embodiment of aself-compensating dynamic balancer which is employed in a disk playeraccording to the present invention;

FIG. 18 is a sectional view taken along line 18—18 of FIG. 17;

FIG. 19 is an exploded perspective view illustrating a turntableincorporating a self-compensating dynamic balancer employed by a diskplayer according to a first embodiment of the present invention;

FIG. 20 is a sectional view of the turntable incorporating aself-compensating dynamic balancer shown in FIG. 19 when a rigid bodyand a fluid are employed as a mobile unit of a self-compensating dynamicbalancer according to the embodiment of the present invention;

FIG. 21 is a sectional view showing a second embodiment of a turntableincorporating a self-compensating dynamic balancer which is employed ina disk player according to the present invention;

FIG. 22 is an exploded perspective view of a first embodiment of aclamper incorporating a self-compensating dynamic balancer which isemployed in a disk player according to the present invention;

FIG. 23 is a sectional view of the damper incorporating aself-compensating dynamic balancer shown FIG. 22 when a yoke is employedas a pressing unit;

FIG. 24 is a sectional view of the clamper incorporating aself-compensating dynamic balancer shown FIG. 22 when a pressing plateand an elastic member are employed as a pressing unit;

FIG. 25 is a sectional view of the damper incorporating aself-compensating dynamic balancer shown FIG. 22 when a rigid body and afluid are employed as a mobile unit;

FIG. 26 is a sectional view showing a second embodiment of a damperincorporating a self-compensating dynamic balancer which is employed ina disk player according to the present invention;

FIG. 27 is an exploded perspective view of a first embodiment of aspindle motor incorporating a self-compensating dynamic balancer whichis employed in a disk player according to the present invention;

FIG. 28 is a sectional view of the spindle motor incorporating aself-compensating dynamic balancer shown FIG. 27 when a rigid body isemployed as a mobile unit;

FIG. 29 is a sectional view of the spindle motor incorporating aself-compensating dynamic balancer shown FIG. 27 when a rigid body and afluid are employed as a mobile unit;

FIG. 30 is a sectional view of a second embodiment of a spindle motorincorporating a self-compensating dynamic balancer which is employed ina disk player according to the present invention; and

FIGS. 31A and 31B are diagrams showing the relationship between theeccentric center of gravity position of a disk, the position of therotational shaft and the ideal center of rotation respectively accordingto different rotational speeds of the disk of the disk player having aself-compensating dynamic balancer according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 2, a disk player according to a preferred embodiment ofthe present invention comprises a deck base 50, a deck plate 70elastically coupled to the deck base 50, buffering members 60 interposedbetween the deck base 50 and the deck plate 70, a spindle motor 100installed at the deck plate 70, a turntable 200 and an optical pickup75, a clamper 300 disposed on a bracket 301 and installed to face theturntable 200 for holding a disk 1 placed on the turntable 200, and aself-compensating dynamic balancer 400 for preventing eccentric rotationof a rotational shaft 130 of the spindle motor 100 due to an eccentriccenter of gravity of the disk 1.

The deck plate 70 receives externally delivered impacts through the deckbase 50 which are alleviated by the buffering members 60. Accordingly,it is preferable that the buffering members 60 are formed of materialexhibiting low rigidity such as soft rubber or polyurethane in order toalleviate external vibrations delivered from the deck base 50. Also, thedeck plate 70 is preferably light in weight for realizingminiaturization thereof. The spindle motor 100 provides a rotationalforce to rotate the disk 1. The center of the turntable 200 is fixed tothe rotational shaft 130 and the disk 1 is placed on the upper surfaceof the turntable 200 during operation. The clamper 300 facing thespindle motor 100 prevents unnecessary movements of the disk 1 placed onthe spindle motor 100. The turntable 200 is fixed to the rotationalshaft 130 and rotated according to the spindle motor 100. Thus, the disk1 and the clamper 300 rotate together.

Referring to FIGS. 3A through 3C, the relationship between the eccentriccenter of gravity position of a disk, the position of the rotationalshaft and the ideal center of rotation according to the rotational speedof the disk will now be described.

FIG. 3A is a diagram schematically showing the orbital and rotationalmovements of the disk when the rate of orbital rotation of the spindlemotor is equal to or less than the natural frequency of the deck plate.In this case, the natural frequency is determined by the elastic modulusof the buffering members and mass of the deck plate and other elementsto be installed on the deck plate, and represents the rate of vibrationin a horizontal direction, i.e., in a direction parallel to the plane ofthe disk. As shown in the drawing, when an eccentric center of gravitym_(e), exists at a position P₁ spaced apart by a predetermined distancefrom the ideal rotation center c₁ of the disk 1, the ideal rotationcenter c₁ of the disk rotates around a center c, moving to positions c₂,C₃ and c₄. The positions of the eccentric center of gravity m_(e) of thedisk corresponding to each of the ideal rotation center positions c₂, C₃and C₄ respectively are p₂, p₃ and p₄. In this case, the respectivepositions p₁, p₂, p₃ and p₄ of the eccentric center of gravity m_(e) andthe revolution center c of the disk 1 are located opposite each otherwith respect to each of the ideal rotation center positions c₁, C₂, C₃and c₄ of the disk 1.

FIG. 3B is a diagram schematically showing the orbital and rotationalmovements of the disk when the rate of revolution of the spindle motoris near the natural frequency of the deck plate. As shown in thedrawing, the revolution center c is located in a direction perpendicularto that of the respective eccentric center of gravity positions p₁, p₂,p₃ and p₄ with respect to positions c₁, C₂, C₃ and c₄.

FIG. 3C is a diagram schematically showing the orbital and rotationalmovements of the disk when the rate of revolution of the spindle motoris greater than the natural frequency of the deck plate, whichcorresponds to the normal rotation speed of a disk allowing informationto be recorded onto or read from the disk. As shown in the drawing, therevolution center c is located in the same direction as the respectiveeccentric center of gravity positions p₁, p₂, p₃ and P₄ with respect topositions c₁, c₂, c₃ and C₄.

In the present invention, it is a characteristic feature that theself-compensating dynamic balancer (400 of FIG. 2) is provided tocompensate for the eccentricity of the disk.

The self-compensating dynamic balancer 400 is incorporated into at leastone of the rotor of the spindle motor 100, the rotational shaft 130, theturntable 200 and the clamper 300 which are rotated by the rotationalforce provided from the spindle motor 100.

As shown in FIGS. 4A and 4B, a first embodiment of the self-compensatingdynamic balancer 400 includes a circular tube 410 whose cross-section isrectangular having a race 450 and a mobile unit 420 movably disposedinside the race 450.

The tube 410 includes a main body 412 through which the race 450 isformed and a cover member 413 for sealing the race 450 in a state inwhich the mobile unit 420 is sealed therein. The tube 410 rotatescoaxially with the rotational shaft 130.

The coupling between the cover member 413 to the main body 412 is madeby using an adhesive, a groove and protrusion assembly formed on thecover member 413 and main body 412 at corresponding positions, or ascrew. The detailed description thereof will be omitted since suchcoupling methods are well known.

The mobile unit 420 includes a plurality of rigid bodies 430 and/or afluid 440 which can move outward from the rotational center by acentrifugal force generated during rotation of the tube 410.

FIG. 5 shows the race 450 in which a plurality of rigid bodies 430 isincluded as the mobile unit 420. Each rigid body 430 is installed to becapable of freely rolling or sliding so that the position thereof can bedetermined by the centrifugal force during rotation of the tube 410.

FIG. 6 shows the race 450 in which a plurality of the rigid bodies 430and the fluid 440 are included.

Since the fluid 440 has a large contact area with the race 450 and thecover member 413 (see FIG. 4) and exhibits a very high viscositycompared to the rigid body 430 only, the fluid 440 employed with therigid bodies 430 in the race 450 can effectively compensate for aninternal vibratory force generated due to the eccentric center ofgravity of the disk 1 (see FIG. 2). That is, the orbital revolution ofthe rotational shaft 130 due to the eccentric center of gravity me ofthe disk can be roughly balanced and reduced by the movements of therigid bodies 430 and finely balanced and reduced by the fluid 440.

The amount of fluid 440 that can be included ranges from an amount whichcoats the outer surface of the rigid bodies 430 to a thickness of only afew microns. In this case, the fluid 440 reduces friction between therigid bodies 430, the race 450 and the cover member 414, rather thanactually contributing to balancing.

As shown in FIG. 7, the second embodiment of the self-compensatingdynamic balancer includes first and second rectangular cross-sectionedtubes 410 a and 410 b arranged concentrically and adjacent to each otherand first and second mobile units 420 a and 420 b respectively disposedinside the first and second tubes 410 a and 410 b to be capable ofmoving.

The respective first and second tubes 410 a and 410 b independentlyserve as a balancer and can finely balance and reduce the orbits of therotational shaft 130. In this case, since each of the first and secondmobile units 420 a and 420 b is actually the same as that of the mobileunit 420 described with reference to FIGS. 5 and 6, a detaileddescription thereof will be omitted.

The first and second tubes 410 a and 410 b and the mobile units 420 aand 420 b respectively installed therein can be configured as shown inFIG. 8. That is, the width and height of the first race 450 a formed inthe first tube 410 a can be configured different from those of thesecond race 450 b formed in the second tube 410 b. Also, the size anddensity of the first and second mobile units 420 a and 420 b located inthe first race 450 a and the second race 450 b, respectively, can bemade different from each other. In this case, since each of the firstand second mobile units 420 a and 420 b is actually the same as themobile unit 420 described with reference to FIGS. 5 and 6, a detaileddescription thereof will be omitted.

When the first race 450 a is formed to have a width and height greaterthan the second race 450 b and the first mobile unit 420 a which isheavier than the second mobile unit 420 b is employed, the first mobileunit 420 a roughly balances and reduces the orbital rotation of therotational shaft 130 due to the eccentric center of gravity m_(e) of thedisk 1, and then the second mobile unit 420 b finely balances andreduces the orbital rotation of the rotational shaft 130.

The self-compensating dynamic balancer described with reference to FIGS.7 and 8 can have two or more tubes.

FIGS. 9 through 11 show different shapes and arrangements of the rigidbody as rigid bodies 430, 430′, and 430″ installed inside the race 450.

FIG. 9 shows a case in which the rigid body 430 is spherical.

FIG. 10 shows a case in which the rigid body is cylindrical. Thecylindrical rigid body 430′ is formed to be capable of rolling with theouter surface of the cylindrical rigid body 430′ contacting the innersurfaces of the inner and outer walls of the race 450. In this case, theupper and lower flat surfaces of the cylindrical rigid body 430′ mayslide in contact with the race 450 generating friction therebetween. Inconsideration of the above, the race 450 preferably has the shape shownin FIG. 16 which will be described later.

FIG. 11 shows a case in which the rigid body is a truncated conic body430″ which can roll with the outer conic surface contacting the bottomsurface of the inside of the race 450.

Also, FIG. 12 shows a case in which the rigid body is a fan-shaped block430′″ which is inserted to be capable of sliding while contacting thebottom surface and the outer circumferential surface inside the race450.

Also, the shape of the rigid body 430 may be modified into other shapesas long as the body can freely move inside the race 450.

Moreover, when being influenced by a magnetic force, there may be apossibility that the rigid body 430 cannot roll smoothly due to magneticattraction. Accordingly, it is preferable that the rigid body 430 isformed of a non-magnetic substance so that the rigid body 430 is notinfluenced by a magnet (not shown).

Preferably, the rigid body 430 is formed of tungsten carbide (WC),beryllium steel (CuBe), Hastelloy C-276, silicon nitride (Si₃N₄),zirconia (ZrO₂), austenite-series stainless steel YHD50, a non-magneticmetal such as SUS300, SUS304 and SUS316, ceramic or a synthetic resin.

As described above, when the rigid body 430 is formed of a non-magneticsubstance, the rigid body 430 is not influenced by a magnetic force froman adjacent magnet. Thus, the rigid body 430 moves dependent only uponthe position of the eccentric center of gravity of the disk 1 (see FIG.2) and the rotation of tube 410.

Further, the rigid body 430 is preferably formed of a non-oxidizingsubstance or anti-oxidation coated, since smooth rolling or sliding ofthe rigid body 430 inside the race 450 will be hindered by oxidation,i.e., corrosion.

For that purpose, the rigid body 430 can be formed of a substance suchas SUS300, ceramic or synthetic resin. Also, the outer surface of therigid body 430 can be anti-oxidation processed by coating a basematerial of carbon steel or chromium steel with zinc or nickel-chromiumplating.

Also, the rigid body 430 can be formed of a substance having fineparticles when oxidized with the air, so that the movement of the rigidbody 430 is not affected.

The shapes of the race 450 and the cover member 413 will now bedescribed with reference to FIGS. 13 through 16.

As shown in FIG. 13, it is preferable that the section through the race450 and the cover member 413 is rectangular. In FIG. 14, thecross-section of the race 450′ and the cover member 413 is an oval.Thus, by reducing the height of the tube 410, the internal vibratoryforce generated during rotation of the tube 410 can be effectivelyalleviated.

Also, as shown in FIG. 15, the cross-section of the race 450″ bulgesinward. Such a case is very appropriate for minimizing the contact areabetween the rigid body 430 and the race 450″.

Further, as shown in FIG. 16, the inner wall of the race 450″′ is formedto be higher than the outer wall so that the upper and lower surficesthe race 450″′ are at an angle. Thus, when the cylindric rigid body 430′(see FIG. 10) is employed, sliding movements of the rigid body 430′inside the race 450″′ can be minimized.

It is preferable that the tube 410 including a race 450 and a covermember 413 are formed of a non-magnetic substance to effectively preventthe influence of a magnetic force between the rigid body 430 and therace 450. That is, the tube 410 and the cover member 413 may be formedof a substance such as tungsten carbide (WC), beryllium steel (CuBe),Hastelloy C-276, silicon nitride (Si₃N₄), zirconia (ZrO₂), brass,aluminum, austenite-series stainless steel YHD50, a non-magnetic metalsuch as SUS300, SUS304 and SUS316, ceramic or a synthetic resin.

Also, the tube 410 is preferably formed of a nonoxidizing substance suchas SUS300, ceramic or a synthetic resin or anti-oxidation coating ofzinc or by nickel-chromium plating over a base material of carbon steelor chromium steel.

As shown in FIGS. 17 and 18, a third embodiment of the self-compensatingdynamic balancer 400 includes a support plate 461 perpendicularly fixedto the rotational shaft 130 and at least one pivoting plate 465hinge-coupled to the support plate 461 being parallel to the same. Inthis case, it is preferable that a pair of the support plates 461 isprovided parallel with each other and the pivoting plate(s) 465 is(are)coupled therebetween. The pivoting plate 465 is pivot-coupled betweenthe support plates 461 by a fixing pin 463.

Referring to FIGS. 19 and 20, a turntable 200 incorporating aself-compensating dynamic balancer according to a first embodiment ofthe present invention will now be described.

A placing member 210 of the turntable 200 is coupled to the rotationalshaft 130 of the spindle motor 100. For that purpose, a coupling hole240 is formed at the center of the placing member 210 so that therotational shaft 130 is inserted into and is fixed to the inside of thecoupling hole 240. A circular locating protrusion 220 which fits throughthe center hole of the disk 1 (see FIG. 2) is formed on an upper surfaceof the placing member 210. The locating protrusion 220 is concentricwith the coupling hole 240. A circular race 250 is formed in the placingmember 210 around the locating protrusion 220. A mobile unit 270 whichincludes rigid bodies 271 that can move away from the rotation center ofthe placing member 210 due to a centrifugal force is inserted into therace 250. The race 250 is sealed by a cover member 260 with the mobileunit 270 inside. After the cover member 260 is assembled onto the upperportion of the placing member 210, the upper surface of the cover member260 is processed to be a flat surface appropriate for contact with thesurface of the disk 1.

The cover member 260 and the placing member 210 are coupled using anadhesive, a groove and protrusion assembly, or a screw. A detaileddescription thereof will be omitted since such coupling techniques arewell-known. As shown in the drawing, an open portion of the race 250 canbe formed on the entire upper surface of the race 250 or on a portion ofthe upper surface thereof being large enough to allow insertion of themobile unit 270 into the race 250.

Also, the turntable 200 preferably includes a magnet 235 to firmly holdthe disk 1 against the surface of the placing member 210 together withthe clamper 300 (see FIG. 2) by a magnetic attraction therebetween. Themagnet 235 is inserted into an installation groove 230 formed betweenthe coupling hole 240 and the locating protrusion 220.

A placing surface 211 processed to be a flat surface to contact thesurface of the disk 1 is provided on upper surface of the placing member210 between the race 250 and the locating protrusion 220. A frictionalmember 213 can be installed to increase the friction between the disk 1and the placing surface 211 to prevent the slip of the disk 1 withrespect to the placing member 210.

The mobile unit 270 comprises a plurality of the rigid bodies 271 and/ora fluid 272 which can be moved away from the center of the placingmember 210 due to the centrifugal force generated during rotation of theplacing member 210.

FIG. 19 shows an example in which a plurality of rigid bodies 271 isincluded as a mobile unit 270 inside the race 250. The rigid bodies 271can freely roll or slide according to the centrifugal force duringrotation of the placing member 210.

As in the embodiment shown with reference to FIGS. 9 through 12, theshape of the rigid body 271 located inside the race 250 is preferablyspherical, cylindrical, has a truncated conic body or is a fan-shapedblock. However, the shape of the rigid body 271 may be modified intoother shapes as long as the body can freely move inside the race 250.

A fluid 272 can be further included together with the rigid body 271 asthe mobile unit 270. Since the fluid 272 has a larger contact area withrespect to the race 250 and the cover member 260 and exhibits a veryhigh viscosity compared to the rigid body 271, the fluid 272 employedwith the rigid body 271 inside the race 250 can effectively compensatefor an inside vibratory force generated due to the eccentric center ofgravity of the disk 1 (see FIG. 2).

The amount of fluid 272 that can be included ranges from an amount whichcoats the outer surface of the rigid bodies 271 to a thickness of only afew microns. In this case, the fluid 272 reduces friction between therigid bodies 271, the race 250 and the cover member 260, rather thanactually contributing to balancing.

When the rigid body 271 is formed of the non-magnetic substance, therigid body 271 is not influenced by the magnetic force from the magnet235 installed inside the locating protrusion 220 or a magnet (not shown)around the placing member 210. Thus, the rigid body 271 moves smoothlydependent only upon the position of the eccentric center of gravity ofthe disk 1 and the rotation of the placing member 210.

Further, the rigid body 271 is preferably formed of a non-oxidizingsubstance or anti-oxidation is coating, since rolling or sliding of therigid body 271 inside the race 250 is hindered by oxidation, i.e.,corrosion. Also, the rigid body 271 can be formed of a substance havingfine particles when oxidized in air, so that the movement of the rigidbody 271 is not affected.

Also, the--fluid 272 can be employed without the rigid bodies 271 as themobile unit 270. In such a case, the cover member 260 and the race 250are sealed to each other to prevent leakage of the fluid 272.

As in the embodiment with reference to FIGS. 13 through 16, the sectionof the race 250 and the cover member 260 is rectangular in shape as at450, an oval 450′, or inwardly bulging 450″. Also, the inner wall of therace 250 is formed to be higher than the outer wall of the same so thata race in which the upper and lower surfaces of the race 250 are at anangle is possible (as in race 450′″).

It is preferable that the placing member 210 including race 250 and thecover member 260 are formed of a non-magnetic substance to effectivelyprevent the influence of a magnetic force between the rigid bodies 271and the race 250. That is, the placing member 210 and the cover member260 are formed of a substance such as tungsten carbide (WC), berylliumsteel (CuBe), Hastelloy C-276, silicon nitride (Si₃N₄), zirconia (ZrO₂),brass, aluminum, austenite-series stainless steel YHD50, a non-magneticmetal such as SUS300, SUS304 and SUS316, ceramic or a synthetic resin.

Also, the placing member 210 is preferably formed of a non-oxidizingsubstance such as SUS300, ceramic or a synthetic resin or ananti-oxidation coating of zinc or by nickel-chromium plating over a basematerial of carbon steel or chromium steel.

Referring to FIG. 21, a turntable 200 incorporating a self-compensatingdynamic balancer according to the second embodiment of the presentinvention will now be described.

As shown in the drawing, the turntable 200 includes a placing member210, a locating protrusion 220 formed to be protruding from the centerof the placing member 210 to insert into the center hole of the disk 1(see FIG. 2), a circular race 250 formed inside the placing member 210,a mobile unit 270 installed to be capable of moving inside the race 250,and a cover member 260 for covering the open portion of the race 250.Here, it is a characteristic feature that first and second races 250 aand 250 b are provided which are formed concentric and adjacent to eachother with respect to the center of the placing member, differently fromthe first embodiment. First and second mobile units 270 a and 270 bshaped as described above are inserted into the first and second races250 a and 250 b, respectively.

The mobile units 270 a and 270 b comprise one of a variously shapedrigid body 271 and/or a fluid 272 as described with reference to FIGS. 9through 12. When the rigid bodies 271 are included as the mobile unit270, it is preferable that the rigid bodies 271 are formed of anon-magnetic substance, a non-oxidizing substance, or is anti-oxidationcoated. Also, the shape of each section of the first and second races250 a and 250 b is one of those described with reference to FIGS. 13through 16.

In this case, it is preferable that the masses of the respective mobileunits 270 a and 270 b inserted in the first and second races 250 a and250 b are different from each other.

This is because of the consideration that a centrifugal force applied tothe mobile unit 270 during the rotation of the placing member 210 isproportional to the respective mass of the mobile unit 270 and thedistance between the center position of the mobile unit 270 and therotation center of the placing member 210. That is, the diameters of thefirst and second races 250 a and 250 b and the mass of the mobile unit270 are determined by considering the allowable error of the eccentriccenter of gravity of the disk.

Although the turntable 200 having two races 250 a and 250 b is describedin FIG. 21, the turntable can be provided with two or more races.

A damper 300 incorporating a self-compensating dynamic balanceraccording to a first embodiment of the present invention will bedescribed in detail with reference to FIGS. 22 through 26.

As shown in FIG. 2, the damper 300 incorporating a self-compensatingdynamic balancer 400 according to the first embodiment of the presentinvention is positioned on the turntable 200 by the bracket 301 coupledwith the deck base 50 and holds the disk 1 in place on the turntable200. Referring to FIGS. 22 and 23, the damper 300 incorporating aself-compensating dynamic balancer 400 of the present invention includesa damper main body 310, a pressing unit 320, a race 350, a mobile unit370 and a cover member 360. The clamper main body 310 is installed onthe deck base 50 to perform a motion relative to the turntable 200. Thepressing unit 320 is installed at the clamper main body 310 to press thedisk 1 in place on the turntable 201. The race 350 is formed inside theclamper main body 310 and is concentric with the rotation center of thedamper main body 310. The mobile unit 370 is installed to be capable ofmoving inside the race 350 and moves toward the outer circumference ofthe clamper main body 310 due to a centrifugal force generated duringthe rotation of the damper main body 310. The cover member 360 coversthe open portion of the race 350.

The cover member 360 and the race 350 are coupled using an adhesive, agroove and protrusion assembly formed at corresponding positions, or ascrew. A detailed description thereof will be omitted since suchcoupling techniques are well-known.

As shown in the drawing, the open portion of the race 350 can be formedon the entire upper surface of the race 350 or on a portion of the uppersurface thereof being large enough to allow the mobile unit 370 to beinserted into the race 350.

The pressing unit 320 can be a yoke 321 coupled to the lower portioninside the damper main body 310 as shown in FIG. 23.

As shown in FIGS. 19 through 21, when the magnet 235 is provided to theturntable 200, the yoke 321 presses the disk 1 (see FIG. 2) using themutual magnetic attraction of the magnet 235.

Also, the pressing unit 320 may be a pressing plate 324 and an elasticmember 325, as shown in FIG. 24. The pressing plate 324 is installed atthe lower surface of the clamper main body 310 to be capable of movingup and down. The elastic member 325 is interposed between the dampermain body 310 and the pressing plate 324 to allow the pressing plate 324to elastically press the disk 1 (see FIG. 2).

Accordingly, when the turntable 200 moves relatively to the clamper mainbody 310, e.g., the turntable 200 is lifted while the clamper main body310 is stationary so that the turntable is in proximity with the clampermain body 310 and the disk 1 placed on the turntable 200 is held by thepressing unit 320. Consequently, the clamper main body 310 rotates,being engaged with the rotating turntable.

The mobile unit 370 includes a plurality of rigid bodies 371 and/or afluid 372 to move away from the rotation center of the rotating clampermain body by the centrifugal force inside the race 350.

FIGS. 22 through 24 show cases in which a plurality of rigid bodies 371are included inside the race 350 as the mobile unit 370. The rigidbodies 371 are installed to be capable of freely rolling or sliding suchthat the position thereof can be determined by the centrifugal forceduring rotation of the placing member.

It is preferable that the rigid body 371 is spherical, cylindrical, hasa truncated conic shape, or is a fan-shaped block, as shown in FIGS. 9through 12. However, the shape of the rigid body 371 may be modified onthe condition that the rigid body 371 can freely move inside the race350.

As shown in FIG. 25, the fluid 372 can be further utilized along withthe rigid bodies 371 as the mobile unit 370. Since the fluid 372 has alarge contact area with respect to the race 350 and the cover member 360and exhibits very high viscosity compared to the rigid bodies 371, thefluid 372 employed with the rigid bodies 371 inside the race 350 caneffectively compensate for an inside vibratory force generated due tothe eccentric center of gravity of the disk 1 (see FIG. 2).

It is preferable that the rigid body 371 is formed of a non-magneticsubstance to be free from the influence of the magnetic force of themagnet 235 (see FIG. 19). In this case, the movement of the rigid body371 is determined dependent only on the eccentric center of gravityposition of the disk 1 and the rotation of the clamper main body 310.

Also, the rigid body 371 is preferably formed of a non-oxidizingsubstance or is anti-oxidation coated to prevent the smooth rolling orsliding of the rigid body 371 inside the race 350 from being hindered byoxidation, i.e., corrosion. Also, the rigid body 371 can be formed of asubstance having fine particles when oxidized in air, so that themovement of the rigid body 371 is not affected.

The fluid 372 can be employed without the rigid bodies 371 as the mobileunit 370.

The shapes of a portion formed by the race 350 and the cover member 360where the mobile unit 370 is a shape described with reference to FIGS.13 through 16. That is, the cross section has a rectangular shape, anoval shape, or an inwardly bulging shape.

Also, it is preferable that the clamper main body 310 including the race350 and the cover member 360 are formed of a non-magnetic substance tobe free from influence of a magnetic force generated between the rigidbodies 371 and the race 350. Further, the clamper main body 310 ispreferably formed of a non-oxidizing substance or is anti-oxidationcoated.

Referring to FIG. 26, the damper 300 incorporating a self-compensatingdynamic balancer 400 according to the second embodiment of the presentinvention will now be described.

As shown in the drawing, the damper 300 includes a damper main body 310,a pressing unit 320 installed at the damper main body 310 and whichpresses the disk 1 (see FIG. 2) in place on the turntable 200, acircular race 350 formed inside the damper main body 310 and concentricwith the rotation center of the damper main body 310, a mobile unit 370installed to be capable of moving inside the race 350, and the covermember 360 for covering an open portion of the race 350. In this case, acharacteristic feature of the present embodiment which distinguishes itfrom the first embodiment is that first and second races 350 a and 350 bformed adjacent to each around the rotation center of the damper mainbody 310 (see FIG. 26) are provided as the race 350.

As described referring to FIGS. 9 through 12, the mobile unit 370includes a rigid body 371 of various shapes and/or a fluid 372. In thecase that the rigid bodies 371 are included as the mobile unit 370, itis preferable that the rigid bodies 371 are formed of a non-magnetic,non-oxidizing substance, or are anti-oxidation coated. Also, thesectional shapes of each of the first and second races 350 a and 350 bare the same as those described earlier referring to FIGS. 13 through16.

It is preferable that each of the mobile units 370 a and 370 brespectively located in the first and second races 350 a and 350 b havea different weight.

This is because of the consideration that the centrifugal force appliedto the mobile units 370 a and 370 b during the rotation of the clampermain body 310 is proportional to the mass of the respective mobile unit370 and the distance between the center of the mobile unit 370 and thecenter of rotation of the damper main body 310. That means that thediameters of the first and second races 350 a and 350 b and the mass ofthe mobile unit 370 a and 370 b are determined considering the allowableerror of the disk eccentric center of gravity.

Although FIG. 26 shows the clamper 300 having two races 350 a and 350 b,it is possible to have two or more races 350 provided to the damperincorporating a self-compensating dynamic balancer 400.

A spindle motor incorporating a self-compensating dynamic balanceremployed in a disk player according to an embodiment of the presentinvention will now be described in detail with reference to FIGS. 27through 30.

The spindle motor incorporating a self-compensating dynamic balanceraccording to the present invention is installed at the deck plate 70 androtates the turntable 200 coupled on the rotational shaft 130, as shownin FIG. 2.

The spindle motor 100 according to a first embodiment of the presentinvention includes a motor base 110, a rotational shaft 130, a stator140, a rotor 120, first and second bearings 132 and 134, a circular race150 integrally formed inside the rotor 120, a mobile unit 170 installedinside the race 150, and a cover member 160 for covering the opening ofthe race 150.

The motor base 110 is coupled with the deck plate 70 (see FIG. 2) andhas a through hole 111. The rotational shaft 130 together with thebearings 132 and 134 inserts into the through hole 111.

The stator 140 is fixed to the bottom surface of the motor base 110 andincludes a yoke 141 facing the rotor 120 and a coil member 143 disposedat the inner side of the yoke 141. The bearings 132 and 134 which aredisposed between the through hole 111 and the rotational shaft 130support the shaft 130 in the radial and axial directions thereof.Accordingly, a pair of the bearings 132 and 134 is provided and disposedinside the through hole 111 separated by a predetermined distance. Thatis, the inner ring of the first bearing 132 is fixed to the rotationalshaft 130 and the outer ring thereof is fixed within the through hole111 so movements in the radial and axial directions of the rotationalshaft 130 are prevented. The second bearing 134 is inserted into thethrough hole 111 to be capable of sliding therein in order to preventthe rotational shaft 130 from being angled. An elastic member 131 isdisposed inside the through hole 111 between the first bearing 132 andthe second bearing 134 to alleviate the rotational vibration of therotor 120 being transmitted to the motor base 110. It is preferable touse a metal bearing as the bearings 132 and 134 considering thepositional accuracy necessary for high-speed rotation. Also, it ispossible to employ other types of bearings such as a ball bearing or adynamic pneumatic bearing.

The rotor 120 includes a case 121 fixed to one end of the rotationalshaft 130 and installed to enclose the stator 140 and a magnet 123 fixedinside the case 121 to surround the yoke 141. A fixing member 133 isfurther included at the coupling between the case 121 and the rotationalshaft 130 to prevent the rotational shaft 130 from slipping off orrunning idly with respect to the case 121.

The race 150 is formed integrally with the case 121, and inside the case121, concentric with the rotational shaft 130. The mobile unit 170 isinstalled to be capable of moving inside the race 150 and moves towardthe outer circumference of the race 150 due to a centrifugal forcegenerated during the rotation of the case 121. The cover member 160covers the opening of the race 150.

The cover member 160 and the race 150 are coupled using an adhesive, agroove and protrusion assembly formed at corresponding positions, orscrews.

The opening of the race 150 can be formed throughout the entire surfaceof the upper surface of the race 150, as shown in the drawing, or formedas part of the upper surface of the race 150, in a size large enough toinsert the mobile unit 170 into the race 150.

The mobile unit 170 comprises a plurality of the rigid bodies 171 and/ora fluid 172 installed to be capable of moving away from the rotationcenter of the rotor 120 inside the race 150 during the rotation of therotor 120.

FIGS. 27 and 28 show a case in which a plurality of rigid bodies 171 isincluded as the mobile unit 170 inside the race 150. The rigid bodies171 are installed to be capable of freely rolling or sliding such thatthe position of the rigid bodies 171 can be determined according to thecentrifugal force generated during the rotation of the rotor 120.

It is preferable that the rigid body 171 is spherical, cylindrical, hasa truncated conic shape, or is a fan-shaped block, as shown in FIGS. 9through 12. Further, the shape of the rigid body 171 may be modified onthe condition that the rigid body 171 can freely move inside the race150.

As shown in FIG. 29, the fluid 172 can be further utilized along withthe rigid bodies 171 as the mobile unit 170. Since the fluid 172 has alarge contact area with respect to the race 150 and the cover member 160and exhibits very high viscosity compared to the rigid bodies 171, thefluid 172 employed with the rigid bodies 171 inside the race 150 caneffectively compensate for an internal vibratory force generated due toan eccentric center of gravity of the disk 1 (see FIG. 2).

It is preferable that the rigid bodies 171 are formed of a non-magneticsubstance to be free from influence of the magnetic force of the magnet123 (see FIG. 27), so that the movement of the rigid bodies 171 isdetermined dependent on the eccentric center of gravity position of thedisk 1 and the rotation of the rotor 120.

Also, the rigid bodies 171 are preferably formed of a non-oxidizingsubstance or are anti-oxidation coated to prevent the smooth rolling orsliding of the rigid bodies 171 inside the race 150 from being hinderedby oxidation, i.e., corrosion. Also, the rigid bodies 171 can be formedof a substance having fine particles when oxidized in air, so that themovement of the rigid bodies 171 is not affected.

The fluid 172 can be employed without the rigid bodies 171 as the mobileunit 170.

The shapes of a portion formed by the race 150 and the cover member 160where the mobile unit 170 is placed is the same as those describedearlier with reference to FIGS. 13 through 16.

Also, it is preferable that the case 121 including the race 150 and thecover member 160 are formed of a non-magnetic substance to be free frominfluence of a magnetic force generated between the rigid bodies 171 anditself.

Further, the case 121 is preferably formed of a non-oxidizing substanceor is anti-oxidation coated.

Referring to FIG. 30, a spindle motor 100 incorporating aself-compensating dynamic balancer employed in a disk player accordingto a second embodiment of the present invention will now be described.

As shown in the drawing, the spindle motor 100 includes a rotation shaft130, a motor base 110, bearings 132 and 134, a stator 140, a rotor 120,a circular race 150 formed inside the rotor 120 and concentric with therotation shaft 130, a mobile unit 170 installed to be capable of movinginside the race 150, and a cover member 160 for covering an opening ofthe race 150. It is a characteristic feature of the present inventionthat first and second races 150 a and 150 b formed adjacent to eachother and concentric with the rotor 120 are provided as the race 150,which distinguishes it from the above-described first embodiment.

Since the shape and material of the mobile unit 170, the race 150 andthe cover member 160 are the same as those described above, a detaileddescription thereof will be omitted.

It is preferable that the weights of mobile units 170 a and 170 binstalled in the first and second races 150 a and 150 b, respectively,are different from each other.

This is because of the consideration that a centrifugal force applied tothe case 121 during rotation of the rotor 120 is proportional to themass of each of the respective mobile units 170 a and 170 b and thedistance between the center of the mobile unit 170 and the rotationcenter of the rotor 120. That is, the diameter of the first and secondraces 150 a and 150 b and the mass of the mobile unit 170 a and 170 bare determined considering the allowable error of the eccentric centerof gravity of the disk 1 (see FIG. 2).

Although a spindle motor 100 having two races 150 a and 150 b is shownin FIG. 30, it is possible to provide a spindle motor incorporating aself-compensating dynamic balancer 100 with two or more races.

As shown in FIG. 2, a disk player according to a first embodiment of thepresent invention includes the deck base 50, the deck plate 70, thebuffering members 60, the spindle motor 100, the turntable 200 and thedamper 300. The turntable incorporating a self-compensating dynamicbalancer 200 is employed as the turntable, as shown in FIGS. 19 through21.

A disk player according to a second embodiment of the present inventionis substantially the same as that of the first embodiment, but a clamperincorporating a self-compensating dynamic balancer 300 as described withreference to FIGS. 22 through 26 is employed.

Also, a disk player according to a third embodiment of the presentinvention is substantially same as that of the first and secondembodiments, but the spindle motor incorporating a self-compensatingdynamic balancer 100 as described with reference to FIGS. 27 through 30is employed.

Further, in the disk player of the present invention as described above,the self-compensating dynamic balancer 400 can be integrally formed withnot just one of the rotating members such as the turntable 200, theclamper 300 and the spindle motor 100 but also two or more of therotating members considering the rotational speed of the disk 1 (seeFIG. 2) and the scope of the allowable error of the position of theeccentric center of gravity.

Hereinafter, the effects of vibration reduction generated when the diskplayer incorporating a self-compensating dynamic balancer and therotating members incorporating a self-compensating dynamic balancer,i.e., the turntable 200, the clamper 300 and the spindle motor 100,according to the present invention are operated, will be described withreference to FIGS. 31A and 31B.

When the angular frequency of the disk 1 is equal to or less than thenatural frequency, as shown FIG. 31A, the position (p_(i),i=1, 2, 3 and4) of the eccentric center of gravity m_(e) of the disk 1 and theposition (p′_(i), i=1, 2, 3 and 4) of a compensated mass m_(c), i.e.,the center of gravity of the self-compensating dynamic balancerincluding the race, the mobile unit and the cover member, are locatedopposite the revolution center c, with respect to the correspondingpositions (c_(i), i=1, 2, 3 and 4) of the rotation shaft. Thus, thedegree of eccentricity of the rotation becomes large.

However, when the angular frequency of the disk 1 is much greater thanthe natural frequency as when the disk rotates at a normal speed, asshown FIG. 31B, the revolution center c and the position (p_(i), i=1, 2,3 and 4) of the eccentric center of gravity m_(e) of the disk 1 arelocated in the same direction with respect to the rotational shaft, andthe position (p′_(i), i=1, 2, 3 and 4) of the compensated mass m_(c) islocated in the opposite direction due to the centrifugal force. Thus, anunbalanced state generated due to the eccentric center of gravity m_(e)of the disk 1 is compensated for and the eccentricity of rotation of therotational shaft is drastically reduced. Consequently, the internalvibratory force of the deck plate due to the eccentric center of gravitym_(e) of the disk 1 is alleviated.

As described above, the disk player incorporating a self-compensatingdynamic balancer, the spindle motor and the rotating members rotated bythe spindle motor according to the present invention compensates for theinternal vibration generated due to the eccentric center of gravity of adisk, by generating a centrifugal force directed from the orbital centerof the disk radially outward which is generated by the mobile unitinside the race. Therefore, the internal vibration generated by theorbital rotation of the eccentric center of gravity of the disk can beeffectively limited.

Also, the disk player according to the present invention employingbuffering members exhibiting a weak rigidity can alleviate externalimpacts. Thus, the disk player according to the present invention isappropriate for a high-speed CD drive of greater than 6X-speed, a CD-ROMdrive, or a DVD drive.

It is contemplated that numerous modifications may be made to the diskplayer of the present invention without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A spindle motor incorporating a self-compensatingdynamic balancer in a disk player, comprising: a rotational shaft; amotor base having a through hole in which said rotational shaft isrotatably inserted; a stator fixedly installed at said motor base andhaving a yoke and a coil wound around said yoke; a rotor having a casewhich is fixed to an end of said rotational shaft and encloses saidstator, and a magnet which is fixed inside said case to face said yoke;at least one circular race which is integrally formed concentric withsaid case and rotates around the center of rotation of said rotationalshaft; a mobile unit located inside said race to be capable of moving;and a cover member which is coupled to an opening of said race forsealing an inner space of said race, wherein the center of gravity ofsaid self-compensating dynamic balancer is located opposite to that of adisk with respect to said rotational shaft of said spindle motor by acentrifugal force generated during rotation of the disk by said spindlemotor, thereby to compensate for vibrations due to an eccentric centerof gravity of the disk.
 2. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 1, wherein saidmobile unit is a rigid body which can roll in said race during rotationof said case.
 3. A spindle motor incorporating a self-compensatingdynamic balancer as claimed in claim 2, wherein, when there is more thanone race, weights of said rigid bodies located in each of said racesdiffer from each other.
 4. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 2, wherein afluid which can flow in said race during rotation of said case isfurther included as said mobile unit.
 5. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 2, wherein saidrigid body is formed of a non-magnetic material in order to avoid beinginfluenced by a magnetic force.
 6. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 5, wherein saidrigid body is formed of a substance selected from the group consistingof tungsten carbide (WC), beryllium steel (CuBe), Hastelloy C-276,silicon nitride (Si₃N₄), zirconia (ZrO₂), brass, aluminum,austenite-series steel YHD50, a non-magnetic metal such as SUS300,SUS304 and SUS316, ceramic and a synthetic resin.
 7. A spindle motorincorporating a self-compensating dynamic balancer as claimed in claim2, wherein said rigid body is formed of a non-oxidizing substance whichdoes not corrode.
 8. A spindle motor incorporating a self-compensatingdynamic balancer as claimed in claim 7, wherein said rigid body isformed of a substance selected from the group consisting of SUS300,ceramic and a synthetic resin.
 9. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 2, wherein anouter circumferential surface of said rigid body is anti-oxidationcoated.
 10. A spindle motor incorporating a self-compensating dynamicbalancer as claimed in claim 9, wherein said anti-oxidation coating isformed of a material selected from the group consisting of zinc andnickel-chromium plated over a base material of carbon steel or chromiumsteel.
 11. A spindle motor incorporating a self-compensating dynamicbalancer as claimed in claim 2, wherein said rigid body is formed in ashape selected from the group consisting of a ball type, a cylindricalbody, a truncated conic body, and a fan-shaped block.
 12. A spindlemotor incorporating a self-compensating dynamic balancer as claimed inclaim 1, wherein said mobile unit comprises a fluid which can flow insaid race during rotation of said spindle motor main body.
 13. A spindlemotor incorporating a self-compensating dynamic balancer as claimed inclaim 1, wherein said case and said cover member are formed of anon-magnetic material in order to avoid being influenced by a magneticforce.
 14. A spindle motor incorporating a self-compensating dynamicbalancer as claimed in claim 3, wherein said case and said cover memberare formed of a substance selected from the group consisting of tungstencarbide (WC), beryllium steel (CuBe), Hastelloy C-276, silicon nitride(Si₃N₄), zirconia (ZrO₂), brass, aluminum, austenite-series steel YHD50,a non-magnetic metal such as SUS300, SUS304 and SUS316, ceramic and asynthetic resin.
 15. A spindle motor incorporating a self-compensatingdynamic balancer as claimed in claim 1, wherein said case and said covermember are formed of a non-oxidizing substance which does not corrode.16. A spindle motor incorporating a self-compensating dynamic balanceras claimed in claim 15, wherein said case and said cover member areformed of a substance selected from the group consisting of SUS300,ceramic and a synthetic resin.
 17. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 1, whereinsurfaces of said case and said cover member facing said rigid body are aanti-oxidation coated.
 18. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 17, wherein saidanti-oxidation coating is formed of a material selected from the groupconsisting of zinc and nickel-chromium plated over a base material ofcarbon steel or chromium steel.
 19. A spindle motor incorporating aself-compensating dynamic balancer as claimed in claim 1, wherein across-section formed by said race and said cover member in which saidmobile unit is located has a shape selected from the group consisting ofa rectangular shape, an oval shape having a longer axis in a latitudinaldirection with respect to the rotational shaft, and an inwardly bulgingpolygonal shape in which a portion of each side bulges inward.